1. Field of the Invention
The present invention relates generally to the art of lead-acid batteries, and more particularly to lead-acid batteries of the oxygen recombinant variety. Still more specifically, the invention relates to a modular frame construction technique, preferably including two compartments for individual battery cell packs. Modularity permits construction of a wide variety of battery designs and capacities, while eliminating the need for expensive housings, tooling and parts inventory.
2. Description of the Prior Art
Recombinant electric storage cells have been known for several years. Generally, such cells contain a reduced amount of electrolyte such that most of it is absorbed into the cell elements (plates and separators) and the cell elements are selected to absorb the gases evolved within the cells. Vents have been provided for the cells to allow excess gas to be vented to the atmosphere, for example, when an overcharge condition occurs during battery formation or when, for some reason, the recombinant efficiency is less than that desired. An example of such a recombinant battery is shown in U.S. Pat. No. 4,618,545 issued Oct. 21, 1986 to Clegg for "Recombination Electric Storage Cells". The patent illustrates a stack of battery elements maintained under a compressive force which is transmitted through special reinforcing members contained in the separators. A major portion of the battery plates are contained by surrounding glass fiber material of the separators.
Recombinant batteries are highly desirable for volume restricted applications where short-duration, high power capability and medium to high cycle life with no maintenance is required. For example, their use in portable powered equipment is known, and several different battery configurations have previously been described in the literature. In some instances these include a film bag for containing the electrodes, separator and electrolyte, a venting system and a system for compression of the film packets to maximize plate and separator contact and to thereby increase the efficiency of the recombinant reactions.
A variety of flattened cell batteries are disclosed in patents assigned to Matsushita Electric Industrial Co., Ltd. One such battery is disclosed in U.S. Pat. No. 4,659,636 issued April 21, 1987 to Suzuki, et al. for "Sealed Storage Battery". In this patent, a plurality of bags, each containing a polar battery plate group, are stacked in a thicknesswise direction and pressurized in a casing. The principal focus of the patent is on the uniform pressure provided by the casing, although the pouch construction and a venting arrangement are shown. The plates and the separators disclosed are of a type which are also applicable to the present invention.
Another patent in this series is U.S. Pat. No. 4,664,994 issued May 12, 1987 to Koike, et al. for "Enclosed Lead Storage Battery And Process For Producing The Same". Here the principal features are the bag or jacket material and the surrounding of the battery posts with an enclosure layer adapted to provide increased sealing efficiency with the jacket. In the preferred embodiments the pole posts are surrounded with a layer of polyolefin and the jacket includes a laminate film with the inner layer being a polyolefin. In this construction, the inner layers of the film can be heat sealed to one another to form the pouch and the posts can be sealed as well. In the disclosed preferred embodiment, the laminate includes three layers, with the outer layer being a material to provide strength, such as a PET, and with an intermediate layer, such as polyvinylidene chloride, which is used to prevent oxygen and moisture permeability. Use of an epoxy resin in the area of the posts to prevent electrolyte leakage is also disclosed. This patent, while describing the bag or pouch, does not discuss the use thereof in multi-bag recombinant electrode systems.
In Kikuchi, et al. U.S. Pat. No. 4,678,725 issued Jul. 7, 1987 for "Hermetically Sealed Storage Battery", another flexible pouch system is disclosed which employs the heat sealing of a peripheral portion of film sheets about the plates of an oxygen recombinant battery plate and separator assembly. The invention disclosed in this patent is a seal which includes a pair of flaps of the film sealed along their edges, but with a channel remaining unsealed to act as an escape vent for gases produced during formation of the battery or for oxygen gas which is produced during battery storage and use and which is not acceptably absorbed by the negative electrodes. In the preferred embodiment, silicone oil is placed in the channel to prevent undesirable ingress of oxygen or moisture.
An oxygen recombinant battery system is also disclosed in U.S. Pat. No. 4,745,039 issued to Yoshinaka on May 17, 1988 for "Sealed Lead Storage Battery". In this patent, the plates are contained in a rigid casing and a breathing hole is provided therein. A safety valve includes a rubber plate over the breathing hole and an elastic pad over the rubber plate urges the plate against the casing. Improved venting of formation gas or excess oxygen produced during use or storage of the battery is alleged.
Finally, another recombinant system is shown in U.S. Pat. No. 4,929,518 issued May 29, 1990 to Yoshinaka, et al. for "Sealed Lead-Acid Storage Battery". In this patent a rigid, frame-like casing of polyolefin material, such as polyethylene, contains positive and negative electrode plates and a separator, the casing surrounding the periphery thereof. Metal plates, laminated with a layer of thermoplastic, are heat welded to the rim of the casing to form an enclosure of the electrode elements, and the terminal posts of the electrodes are provided with epoxy-resin and polyolefin coatings similar to those described earlier. A vent is arranged over a breathing hole in the casing, the vent including a flat rubber sheet in contact with the surface containing the hole, and a layer of cushion material is compressed thereover by a pressing plate. The pressing plate is adapted to create sufficient pressure on the rubber sheet to prevent gas escape from the casing except during periods of excessive gas pressure (i.e. pressures derived from formation gas or inefficient absorption of oxygen by the negative electrode).
While certain concepts and constructions used in the aforementioned patents will be used as well in the battery of the present invention, many of the aforementioned devices suffer from one or more drawbacks. Principally, the devices still require a specially designed outer casing for those which employ more than one cell pack, and they do not provide design flexibility or eliminate the need for large inventories of bulky battery housings. A modular electrode design which would permit construction of a variety of batteries of various voltages and sizes would represent a substantial advance in the art.